Shaft pre-heater

ABSTRACT

A shaft preheater to achieve an improved adaptation of layer height to particle size spectrum of material to be preheated. The shaft preheater includes a plurality of shafts for receiving lumpy material, an arrangement for filling the individual shafts with the lumpy material to be preheated and means for limiting the layer height in the shafts. The means for limiting the layer height include a needle valve and have an arrangement for coarse adjustment and an arrangement for fine adjustments.

FIELD OF THE INVENTION

The invention relates to a shaft preheater with a plurality of shaftsfor receiving lumpy material, an arrangement for filling the individualshafts with the lumpy material to be preheated and also means forlimiting the layer height in the shafts.

BACKGROUND OF THE INVENTION

Particularly in the calcination of materials in large lumps, such as forexample limestone, dolomite or magnesite, with a feed particle sizebetween 15-60 mm, rotary kilns are frequently used. In order to increaseefficiency, shaft preheaters are often disposed upstream of these rotarykilns. Preheating and partial calcination of the lumpy material takesplace in the shaft preheater using the exhaust gases from the rotarykiln. For an efficient heat exchange and in order to maintain aneconomical pressure loss there must be a good throughflow of thegranular mass of material. Therefore the ratio between maximum andminimum fragment size of the feed particles is limited to 1:3. Thus forexample a particle size spectrum of 15-45 mm or 20-60 mm can be treatedin the shaft preheater. However, a greater particle size spectrum occursin quarrying, so that the kiln system is operated correspondingly instages.

In order to ensure a good throughflow of the granular mass of materialit is necessary to adapt the layer height to the particle size spectrumof the material to be preheated. Thus a coarser particle size spectrummakes possible a greater layer height than a smaller particle sizespectrum of the material to be preheated.

Therefore in order to process different particle size spectra it isknown to provide means for limiting the layer height in the shafts. Forexample, it is known in the art for the covers of all shafts to beadjusted in height in order thereby to limit the layer height.

However, these known means for limiting the layer height are veryexpensive and, moreover, always only one particle size spectrum can beprocessed in the shaft preheater.

A shaft preheater which consists of kiln feed shafts disposedpolygonally around a gas inlet shaft is known from DE-B-27 48 670. Eachkiln feed shaft can have its own layer height control independently ofthe others.

SUMMARY OF THE INVENTION

The object of the invention is to improve the shaft preheater in such away that it makes possible an improved adaptation of the layer height tothe particle size spectrum of the material to be preheated.

The shaft preheater according to the invention includes a plurality ofshafts for receiving lumpy material, an arrangement for filling theindividual shafts with the lumpy material to be preheated and also meansfor limiting the layer height in the shafts, the means being constructedin such a way that a separate adjustment of the layer height is providedat least in some shafts. The means for limiting the layer height have anarrangement for coarse adjustment and an arrangement for fine adjustmentof the layer height.

If the arrangement for fine adjustment of the layer height is formed bya needle valve, this can be actuated during the operation of the shaftpreheater in order to adapt the layer height.

In a preferred embodiment separate means for limiting the layer heightare provided in all shafts.

According to one embodiment the means for limiting the layer heightcomprise a slide plate which can be introduced, particularly from above,into the corresponding shaft and of which the lower edge serves forlimiting the layer height.

The shaft preheater has in a manner which is known per se means forintroducing a hot gas stream into the shafts as well as means fordrawing off the hot gas stream which is led through the material layerinto the individual shafts. In a particular embodiment of the invention,moreover, a measuring device is provided within a shaft in order todetermine the pressure loss of the hot gas stream, the means forlimiting the layer height being controllable as a function of thepressure loss.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and embodiments of the invention are explained ingreater detail with reference to the following description of anembodiment and the drawings, in which:

FIG. 1 shows a schematic longitudinal sectional view of the shaftpreheater,

FIG. 2 shows a sectional view along the line II—II in FIG. 1, and

FIG. 3 shows an enlarged partial view of FIG. 1 in the region of ashaft.

DETAILED DESCRIPTION OF THE INVENTION

The shaft preheater consists essentially of a feed bin 1 which isdivided into a plurality of sectors 1 a, 1 b, . . . which are eachadjoined below by one of a plurality of shafts 2 a, 2 b,

The individual shafts are filled via the feed bin with the lumpymaterial 4 which is to be preheated.

The feed bin 1 is divided symmetrically or asymmetrically intoindividual sectors according to the number of particle size spectraoccurring. In the case of asymmetric division, the filling arrangement 3is formed for example by a swivelling chute. If only two differentparticle size spectra are to be treated, then a symmetrical division ofthe feed bin 1 would be appropriate. The feeding then takes placealternately via a changeover valve 3 a. The distribution in the feed bin1 to the individual shafts 2 a, 2 b, . . . takes place using the naturalangle of repose of the slope.

The preheating and optionally partial calcination of the lumpy materialtakes place in the individual shafts 2 a, 2 b, . . . which are disposedaround a central axis 5 of the shaft preheater. In principle there canbe any number of individual shafts, but there are usually between sixand twenty shafts. The lumpy material 4 which is preheated in the shaftpreheater proceeds via an inlet housing 6 into a rotary kiln 7. For thispurpose discharge means, for example in the form of rams, are providedin the lower region of the shafts. The flue gases from the rotary kilnare drawn upwards from below through the individual shafts 2 a, 2 b incounter-current flow to the material 4 and thus through the granularmass of material. Therefore suitable means are provided in the lowerregion of the individual shafts in order to introduce into theindividual shafts 2 a, 2 b the flue gases led out of the rotary kiln 7via the inlet housing 6. The hot gas stream formed by the flue gas heatsthe lumpy material located in the shafts and is drawn off in the upperregion of the shafts via means 8. The means 8 are formed by suitableducts 8 a, 8 b which open into the upper region of the shafts 2 a, 2 b.

Since different particle size spectra have correspondingly differentpressure losses and heat transfers, it is necessary to adapt the layerheight in the individual shafts to the particle size spectrum locatedtherein. For this purpose at least some, and preferably all of theshafts have means 9 for limiting the layer height, wherein a separateadjustment of the layer height in these shafts is possible.

FIG. 3 shows an enlarged representation of the shaft 2 b in the regionof the means 9 for limiting the layer height. The means 9 consistsessentially of an arrangement 90 for coarse adjustment and anarrangement 91 for fine adjustment of the layer height. The means 90 forlimiting the layer height are formed in the illustrated embodiment by aslide plate which can be introduced from above into the shaft 2 b and ofwhich the lower edge 90 a serves for limiting the layer height. Theslide plate can be displaced in the vertical direction by a mechanismwhich is not shown in greater detail.

In the illustrated embodiment the means 91 are formed by a needle valvehaving a plurality of rods which are disposed in two rows offset withrespect to one another, as can be seen in particular from FIG. 2.

FIG. 2 also shows that the shaft 2 b has a rectangular cross-section,particularly a square cross-section. The means 90, 91 for limiting thelayer height are disposed so that they delimit more than half,preferably approximately a third of the shaft, the lumpy material 4being delivered via this delimited region of the shaft. Thus the lumpymaterial 4 has the full cross-section of the shaft 2 a available onlyfrom the lower edge 90 a of the slide plate or the lower edge 91 a ofthe needle valve 91. Below these lower edges the lumpy material 4 willdistribute itself according to the natural angle of the slope surface.In the shaft 2 a of FIG. 1 three slope surfaces denoted by the referencenumerals 4 a, 4 b and 4 c are shown which can form at differentpositions of the layer height limiting means 9.

The slide plate 90 which serves for coarse adjustment of the layerheight is identified by computer and adjusted before the preheater isput into operation. The needle valve 91 which serves for fine adjustmentof the layer height, the rods of which are tapered at the lower end, canalso be adjusted during operation so that fine adjustment is possible inaccordance with the actually occurring pressure loss. In this way it ispossible to achieve a uniform throughflow of gas over the entirepreheater even when different particle size spectra and thus differentlayer heights must be set in the individual shafts.

A measuring device for determining the pressure loss of the hot gasstream within the shaft is advantageously associated with each shaft.The means 9 for limiting the layer height are then controlled as afunction of the pressure loss.

The hot gas stream which is formed by the flue gas from the rotary kilnand flows upwards from below through the individual shafts takes thepath of least resistance in the region of the layer height limitingdevice 9 and thus leaves the granular mass of material in the region ofthe inclined slope surfaces which have been produced below the loweredges of the layer height limiting device 9. The hot gas stream is thendrawn off via the discharge means 8.

The layer height limiting device 9 is designed so that introduction ofthe slide plates 9 can be dispensed with if the preheater is operatedwith the coarsest particle size spectrum.

1. A shaft preheater, comprising: a plurality of shafts for receivinglumpy material; an arrangement for filling the individual shafts withthe lumpy material to be preheated; and means for limiting the layerheight in the shafts, said means being constructed, in such a way that aseparate adjustment of the layer height is provided at least in someshafts; said means for limiting the layer height include a needle valveand have an arrangement for coarse adjustment of the layer height and anarrangement for fine adjustment of the layer height.
 2. A shaftpreheater as claimed in claim 1, wherein separate means for limiting thelayer height are provided in all shafts.
 3. A shaft preheater as claimedin claim 1, further comprising a feed bin through which the individualshafts are filled with lumpy material, the feed bin being divided intoindividual sectors.
 4. A shaft preheater as claimed in claim 1, whereinsaid means for limiting the layer height comprise a slide plate.
 5. Ashaft preheater as claimed in claim 1, wherein said means for limitingthe layer height comprise a slide plate which can be introduced fromabove into the corresponding shaft and of which the lower edge servesfor limiting the layer height.
 6. A shaft preheater as claimed in claim1, wherein said needle valve can be actuated during operation of theshaft preheater.
 7. A shaft preheater as claimed in claim 1, furthercomprising: means for introducing a hot gas stream into the shafts; andmeans for drawing off the hot gas stream led through the material layerinto the individual shafts.
 8. A shaft preheater as claimed in claim 1,further comprising: means for introducing a hot gas stream into theshafts; means for drawing off the hot gas stream led through thematerial layer into the individual shafts; and a measuring device fordetermining the pressure loss of the hot gas stream provided within theshaft; wherein the means for limiting the layer height are controllableas a function of the pressure loss.